The present invention relates to a method and system for controlling the spark ignition of spark plugs, in the ignition system of a multi-cylinder four-stroke internal combustion engine.
The present invention has particular application for controlling the spark ignition in at least two cylinders of the foregoing type of engine, wherein the pistons of such cylinders simultaneously assume a top dead center position, and wherein an ignition capacitor operates in conjunction with at least two discharging circuits and one charging circuit. The discharging circuits each comprise, in series, a primary winding of an ignition coil and a first circuit breaker element which can be switched from an electric control unit. The charging circuit supplied with current from a direct-current source, comprises a coil in series with a second circuit breaker element which can be switched from the control unit.
An engine as specified above can comprise, for example, a four-cylinder Otto-cycle engine in which the electric control unit included in the ignition system replaces a conventional mechanically controlled ignition distributor. Some of the electric control unit lacks a cam shaft transmitter, it is not possible to initially determine which cylinder is the first one to be in firing position. To ensure that ignition voltage is generated in the cylinder which is in firing position, it is suggested to allow the control unit to trigger ignition at the same time in two or all cylinders as soon as the signal from a crank shaft transmitter indicates that the pistons in a pair of cylinders assume the top dead centre position. In this arrangement, the charge of the ignition capacitor is utilized for simultaneous ignition in two or more cylinders and, as a result, only half or less than half of the charge of the ignition capacitor is used for generating ignition sparks in a cylinder.
If the voltage of the direct-current source drops due, for example, to low environmental temperatures, special starting problems occur with engines of the type just described. Thus, a low source voltage can result in the control unit not being able to properly control the charging processes occurring during a starting procedure.
Through German Patent Specification No. 2 448 302, a method and system are already known for assuring, during the start of an internal combustion engine, the charging of an ignition capacitor even with a decreasing battery voltage. But this does not teach how to arrange the charging and discharging of the ignition capacitor to obtain a more reliable ignition when starting an engine of the type as specified above.